Bishop of London and third Archbishop of Canterbury, d. 24 April, 624. He was the leader of the second band of missionaries whom St. Gregory sent from Rome to join St. Augustine at Canterbury in 601. Venerable Bede (Hist. Eccl., II, vii) describes him as of noble birth, and as he is styled abbot by the pope (Epp. Gregorii, xi, 54, 59), it is thought he may have been Abbot of the Monastery of St. Andrew on the Coelian Hill, to which both St. Gregory and St. Augustine belonged. Several commendatory epistles of the pope recommending Mellitus and his companions to various Gallic bishops have been preserved (Epp., xi, 54-62). With the band he sent also "all things needed for divine worship and the Church's service, viz. sacred vessels and altar cloths, vestments for priests and clerics, and also relics of the holy apostles and martyrs, with many books" (Bede, "Hist. Eccl.", I, 29).

The consecration of Mellitus as bishop by Augustine took place soon after his arrival in England, and his first missionary efforts were among the East Saxons. Their king was Sabert, nephew to Ethelbert, King of Kent, and by his support, Mellitus was able to establish his see in London, the East Saxon capital, and build there the church of St. Paul. On the death of Sabert his sons, who had refused Christianity, gave permission to their people to worship idols once more. Moreover, on seeing Mellitus celebrating Mass one day, the young princes demanded that he should give them also the white bread which he had been wont to give their father. When the saint answered them that this was impossible until they had received Christian baptism, he was banished from the kingdom. Mellitus went to Kent, where similar difficulties had ensued upon the death of Ethelbert, and thence retired to Gaul about the year 616.

After an absence of about a year, Mellitus was recalled to Kent by Laurentius, Augustine's successor in the See of Canterbury. Matters had improved in that kingdom owing to the conversion of the new king Eadbald, but Mellitus was never able to regain possession of his own See of London. In 619, Laurentius died, and Mellitus was chosen archbishop in his stead. He appears never to have received the pallium, though he retained the see for five years-a fact which may account for his not consecrating any bishops. During this time, he suffered constantly from ill-health. He consecrated a church to the Blessed Mother of God in the monastery of SS. Peter and Paul at Canterbury, and legend attributes to him the foundation of the Abbey of St. Peter at Westminster, but this is almost certainly incorrect. Among the many miracles recorded of him is the quelling of a great fire at Canterbury which threatened to destroy the entire city. The saint, although too ill to move, had himself carried to the spot where the fire was raging and, in answer to his prayer, a strong wind arose which bore the flames southwards away from the city. Mellitus was buried in the monastery of SS. Peter and Paul, afterwards St. Augustine's, Canterbury. Some relics of the saint were preserved in London in 1298. The most reliable account of his life is that given by Bede in "Hist. Eccl.", I, 29, 30; II, 3-7. Elmham in his "Historia Monasterii S. Augustini Cantuar.", edited by Hardwick, gives many additional details, but the authenticity of these is more than questionable. His feast is observed on April 24.